This invention relates to a novel human integrin .beta. subunit protein, .beta..sub.5, DNA encoding this protein, and to methods for detection and/or quantification of .beta..sub.5. In one embodiment this includes detecting .beta..sub.5 protein in the biological fluids or tissues of humans using antibodies which are capable of binding to this protein.
The integrin family consists of at least 14 distinct cell surface heterodimers that are involved in cell-cell and cell-extracellular matrix adhesion functions (Ginsberg, et al., (1988) Thrombos. Hemostas., 59:1-6); Kishimoto, et al., (1989b) Adv. Immunol., 46:149-182; Ruoslahti, (1988) Annu. Rev. Biochem., 57:375-413; Hemler, (1990) Annu. Rev. Immunol., 8:365-400). The integrins were originally divided into three subfamilies, each having a characteristic .beta. chain that associates with multiple .alpha. subunits (Hynes, (1987) Cell, 48:549-554). The VLA protein family (sharing a common .beta..sub.2 subunit) has three members involved in leukocyte cell-cell adhesion (Kishimoto, et al., (1989b) Adv. Immunol., supra); and the cytoadhesion family (sharing the .beta..sub.3 subunit) consists of the platelet IIb-IIIa complex and the vitronectin receptor, which adhere to a variety of extracellular matrix proteins (Ginsberg, et. al., (1988) Thrombos. Hemostas., supra).
Recently, the discovery of additional .beta. subunits has added to the complexity within the integrin family. For example, the .alpha..sup.6 subunit associates not only with .beta..sub.1, but also with a newly described .beta..sub.4 subunit (Hemler, et al., (1989) J. Biol. Chem., 264:6529-6535; Kajiji et al., (1989) EMBO J., 8:673-680). Compared to .alpha..sup.6 .beta., which has widespread distribution, .alpha..sup.6 .beta..sub.1 is prevalent on normal neoplastic epithelial cell types (Hemler, et al., (1989) J. Biol. Chem., supra) and aligns with basement membranes in many tissues (Kajiji, et al., (1987) Cancer Res., 47:1367-1376). Similarly, on a subset of mouse lymphocytes, the mouse .alpha..sup.4 subunit associated with .beta..sub.p instead of .beta..sub.1, and the .alpha..sup.4 .beta..sub.p complex functions as a receptor for high endothelial venules in Peyer's patches (Holzmann, et al., (1989) Cell, 56:37-46; Holzmann and Weissman, (1989) EMBO J., 8:1735-1741). While the .alpha..sup.4 .beta..sub.1 (VLA-4) complex might also bind to Peyer's patches (Holzmann and Weissman, (1989) EMBO J., supra), it has multiple other adhesive functions (Elices, et al., (1990) Cell, 60:577-584). The .alpha..sup.v subunit of the vitronectin receptor has reported to associate with two additional .beta. subunits besides .beta..sub.3. A complex called .alpha..sup.v .beta..sub.x was identified from lung carcinoma cells, using an anti-.alpha..sup.v monoclonal antibody (mAb) (Cheresh, et al., (1989) Cell, 57:59-69). The .beta..sub.x subunit was chemically distinguishable from the .beta..sub.3 subunit which is usually associated with .alpha..sup.v on endothelial cells and other cell types (Cheresh, et al., (1989) Cell, supra). However, the .beta..sub.x subunit has not been fully elucidated. On MG 63 osteosarcoma cells and fibroblasts, a subunit called .beta..sub.s was found to be associated with .alpha..sup.v, and the .beta..sub.s subunit underwent a marked serine phosphorylation upon treatment of MG63 cells with a tumor promoter PMA (Freed, et al., (1989) EMBO J., 8:2955-2965). Although .beta..sub.s is antigenically and biochemically distinct from .beta..sub.3, it is not yet certain that it is distinct from .beta..sub.x. One problem has been that neither cDNA probes nor antibody reagents have been available for use in direct characterization of .beta..sub.x (or .beta..sub.s).
At this time the .beta..sub.p, .beta..sub.4, .beta..sub.x (and .beta..sub.s) subunits each are known to associate with only one known .alpha. subunit, and thus do not appear to define new integrin families. Instead, they replace the prototype .beta..sub.1 and .beta..sub.3 heterodimers on certain cell types.
Among the .beta. subunits, genes for human .beta..sub.1 (Argraves, et al., (1987) J. Cell Biol., 105:1183-1190), .beta..sub.2 (Kishimoto, et al., (1987) Cell, 48:681-690; Law, et al., (1987) EMBO J., 6:915-919) and .beta..sub.3 (1988) Blood, 72:593-600 have been cloned and sequenced, and show 44-47% homology to each other, with complete conservation of all of their 56 cysteines. Also, the .beta..sub.1 subunits from human (Argraves, et al., (1987) J. Cell Biol., supra. mouse (Tominaga, (1988) FEBS Letters, 238:315-319; Holers, et al., (1989 J. Exp. Med., 169:1589;14 1605) chicken (Tamkun, et al., (1986) Cell, 46-271-282) and frog (Desimone and Hynes, 1988) J. Biol. Chem., 263:5333-5340) show 82-90% homology, emphasizing the importance of this molecule throughout vertebrate evolution.
From their primary structures, it is evident that each of the integrin .beta. subunits is a transmembrane protein, with a large extracellular domain and a short cytoplasmic tail. Within the extracellular domain, the region near amino acids 100-140 has a particularly high degree of conservation. In addition, RGD-peptide crosslinking studies have implicated that same region as a potential ligand binding site (D'Souza, et al., (1988) Science, 242:91-93; Smith and Cheresh, (1988) J. Bio. Chem., 263:18726-18731).
The cytoplasmic domain of .beta..sub.1 has been shown to bind to the cytoskeletal protein talin (Horwitz, et al., (1987) Nature, 320:531-533) and a newly described protein called fibulin (Argraves, et al., (1989) Cell, 58:623-629). These cytoskeletal interactions may be critical for the function of integrins as transmembrane receptors, linking extracellular matrix ligands with the cytoskeletal framework. The cytoplasmic domains of the known .beta. subunits are highly dissimlilar, suggesting that each interacts with the cytoskeleton in a specific manner.
Several .beta. subunits have been found associated with carcinomas. Specifically, the expression of .beta..sub.4 in mouse (Falcioni et al., (1986) Cancer Res., 46:5772-5778) and human cells (Kimmel and Carey, (1986) Cancer Res., 46:3614-3623) has been correlated with tumor cell aggressiveness.
It would be useful to have an additional determinant for detecting the presence of carcinomas.
In addition, it would be useful to have a means by which to distinguish different cell types.